In the art of liquid filtration, one of the methods for separating solids slurried in liquids in large open tanks is to use a filter known in the art as a filter leaf assembly. Typically, one drops one or more large, usually rectangular, filter frames covered by a filter cloth or bag into the tank, draws a vacuum within the filter bag to draw the liquid to be filtered inside the bag, and pumps the liquid out of the bag. Each filter frame is lifted out of the tank periodically when it has become so loaded with solids as to reduce the filtration rate to an ineffective or uneconomic extent, and the solids are then knocked off by vibration, scraping, washing, shaking or other methods known in the art, the cake collected or concentrated in the filter apparatus, and the filter cycle repeated.
The filter bag used over the frame is usually a woven filter cloth, sewn at intervals into pockets which contain long molded plastic or metal stays or shapes inserted into the pockets to hold the cloth apart, to resist pressure, and to stiffen the bag.
The stays are as long as the filter cloth, molded into a shape which has channels or grooves for the liquid being filtered to flow within, and at the same time molded into a shape which is inherently strong enough to resist the pressure on the outside of the filter when it is nearly clogged by a thick cake of solids.
The support frame is usually rectangular, supports the pocketed envelope shaped filter cloth, the drain channel stays or shapes, and a filtrate receiver collector which may be a wood, metal, or plastic header or manifold. The top of the filter cloth is gathered and sealed for a vacuum-tight closure to the filter assembly on this header or manifold. A typical example of this type of filter is a Diastar tradenamed filter apparatus developed by Filters Gaudfrin (France). Also known are Moore filters, of similar construction, which have been used in gold mining and the sulfate process for titanium dioxide.
All the presently known filter leaf assemblies, where reversed flow is used, have in common a number of problems. The filter cloth has to be sewn to form pockets to hold drain inserts which prevent the filter cloth from collapsing under pressure. The drain inserts themselves block off some of the flow of filtrate. Needle holes from sewing must be sealed to prevent filtrate leakage. This can be expensive and time consuming. Since many pockets are needed to provide adequate drainage, sewing itself becomes expensive. Also, standard filter media such as felts and cloths tend to clog with solids which penetrate into the interstices to cause high operating pressures and reduced through-put.
Also known are ridged and corregated plates, sometimes manufactured from nets of expanded metal sheets, which can be inserted into filter bags for similar filtration as disclosed by Roos U.S. Pat. No. 4,256,586.
Other types of corregated filter media are known, such as the filter panels of Bourdale, as shown in U.S. Pat. Nos. 3,358,843 and 3,279,616, which are useful in filter cartridges.
Corregated plates have been used between filter elements in stacked annular filter arrangements, such as those provided by Gutkowski U.S. Pat. No. 3,209,915.